Uninterruptible Power Supplies
(UPS) are electronic based power backup systems,
capable of providing short term supply of high quality
and stabilized electrical power, without interruption
to operations.

There are various types of
UPS available, the vast majority of which use a
battery string to feed an inverter which takes the
DC voltage, inverts the voltage to AC, and then
manufactures and regulates an output voltage, independent
from the input mains.

UPS equipment is very
economic for relatively short periods of time which
generally allow for sufficient time to ride our
any short term disturbances or interruptions, and
where required, allow for a proper and orderly shutdown
of the connected critical connected equipment.

Where extended backup times are required,
this can be provided through over sizing the UPS,
adding additional battery packs, or engineering
appropriately rated battery strings of sufficient
ampere hour capacity, although to support equipment
for longer autonomy periods, it can often be more
economical to provide a generator, to be used in
conjunction with the UPS.

UPS provide
2 main advantages:

• They filter many
unwanted electrical disturbances from the mains
power supply

• They supply an uninterrupted
power to the connected loads in the event that the
mains power supply fails.

But also be aware
of their disadvantages, as UPS are often given a
greater kudos, than what they can actually provide!

It is commonly misunderstood that Uninterruptible
Power Supplies provide the highest possible level
of surge protection available, to connected critical
loads from power surges including lightning transients,
where in reality, this is far from reality.

Whilst it is true that some UPS equipment provides
a degree of isolation and surge filtering, this
is typically limited to internal RF filtering components
which are unlikely to attenuate transients that
are brought about through lightning activity which
are very high dV/dT and dI/dT, and are of a completely
different bandwidth to power frequencies

Lightning, for example, is typically between
5 to 50 kHz.

Online UPS are themselves
highly susceptible to damage caused by lightning
transients, due to the inherent fact that UPS systems
are themselves heavily semi conductor based, and
are therefore subject to the same damaging and deleterious
effects as brought about by lightning transients,
as are the critical loads they are often charged
with protecting.

UPS systems where never
intended to be subjected to the level of transient
energy contained in lightning currents, which are
only addressed by using specific surge protection
componentry such as MOVS followed by L-C wired filter
components. Most well respected UPS manufacturers
actually state in their product specifications (if
at all) a maximum Rectifier input surge rating of
ANSI C41.62 Cat B, which is 6kV 1.2/50us: 3 kA @
8/20us.

Lightning transients regularly
exceed these levels.

What is more disturbing
is that UPS systems often include an internal static
bypass as standard inclusion in their design, which
automatically transfers the critical load over to
raw mains, in order to protect the UPS in the event
of a fault conditions, depleted battery autonomy,
or during repair or annual maintenance requirements.

In mission critical environments, this is a
major weakness, as the UPS can and will transfer
the critical load over to unprotected raw mains,
which usually occurs during times of questionable
conditions, such a thunderstorms. This clearly is
the time of greatest risk to the critical loads,
and is exactly the time when the critical loads
should have maximum amount protection. By the provision
of the bypass, the UPS shows its true colours as
a surge protector, by removing all protection from
the critical load for no other reason but to protect
itself.

UPS systems also fail/transfer
to bypass when:

• Mains power is removed
periodically or completely, causing battery life
to be exhausted, where the unit will then shut down
automatically, transferring the load to unprotected
raw mains.

• Power system faults may cause
the UPS to transfer to bypass, in order to protect
itself, thereby transferring critical load to raw
mains and removing any protection placing equipment
on raw mains..

• Lightning transients often
damage the rectifier/charger component, thereby
transferring the load to the bypass, further requiring
UPS to be put in maintenance bypass, or even completely
removed from the circuit for off site repair. No
protection is provided to the critical loads in
either static or maintenance bypass modes.

It is our recommendation that ALL UPS equipment
be powered from a suitably rated Surge Reduction
Filter, where the UPS will be offered the protection
it requires, and secondly where the UPS fails, or
is removed for maintenance, or goes to bypass, the
critical loads will subsequently still be protected
from mains borne transients.